I have gone through lots of HRMs over the years, Garmin Dual Band, Wahoo Tickr, Magene H303, but all seem to have the same problem. They work really well on the original battery but once you change it, the waterproofing degrades and then they start playing up.
So the Xoss X2Pro is a revelation - its rechargeable! Work really well, has LED lights, audible warnings, have used it every day for 3 months with a few 5 hour days on the bike in there - no drop outs and totally reliable results.